Scale, volume, chargeable
Scale weight is what your kitchen scale would print; volumetric weight is the space the parcel occupies converted into kilograms; chargeable weight is whichever of the two costs more, rounded up to the next half kilogram. A 3.2 kg parcel measuring 46 by 34 by 22 cm came out at 5.74 kg raw volumetric, 6.0 kg rounded at a divisor of 6000 and 7.0 kg rounded at a divisor of 5000, so the same box has three defensible weights depending on which figure you quote.
Define every variable before you calculate anything, because the divisor is the single input people leave unstated. Length, width and height go in centimetres, the divisor is 5000, 6000 or 8000 depending on the line, the scale weight goes in kilograms, and the rounding step is fixed at 0.5 kg upward. Write those five items at the top of the page and the rest of the calculation stops being ambiguous.
Three figures compete for the same parcel, and only two of them reach the settlement line. Scale weight is the sealed carton on a calibrated platform, volumetric weight is length times width times height in centimetres divided by the line's divisor, and chargeable weight is the larger of the two pushed up to the next 0.5 kg. Density settles who wins: at divisor 6000 the crossover sits at 1 kg per 6,000 cm³, roughly 167 kg/m³, while divisor 5000 raises the bar to 200 kg/m³ and divisor 8000 lowers it to 125 kg/m³, all three read off the divisors we recorded in 12 rate snapshots taken between 2026-08-01 and 2026-10-02 (Recorded). Work the step boundary as well as the crossover, because the 0.5 kg ceiling hides small wins: at divisor 6000 the 3.5 to 4.0 kg step sits exactly at 21,000 cm³, so 21,000 cm³ bills 3.5 kg while 21,600 cm³ bills 4.0 kg, and that 600 cm³ gap is worth 0.5 kg, or £2.63 at the £5.26 per kilogram our £120 consignment paid (Recorded). Below the crossover, compress the carton; above it, pay the volume and stop measuring.
Cubage over constant
Volumetric kilograms equal length times width times height divided by the divisor. Chargeable kilograms equal the ceiling of the larger of scale weight and volumetric weight, taken up to the next 0.5 kg. The uplift is the chargeable figure minus the rounded scale weight, and the uplift percentage is that difference divided by the chargeable figure, multiplied by 100.
Worked once with the 3.2 kg parcel: 46 times 34 times 22 is 34,408 cubic centimetres. Divided by 6000 that is 5.735 kg, which rounds to 6.0 kg. The scale weight of 3.2 kg rounds to 3.5 kg, so the uplift is 2.5 kg, or 41.7% of the bill. Change the divisor to 5000 and the chargeable figure becomes 7.0 kg with a 3.5 kg uplift, which is 50.0% of the bill.
Measuring decides most of the bill, so run two checks before the calculator opens and one after. 1. Square the box up, then read each side at its widest point with the tape flat, because a 1 cm bulge on the height of a 46 by 34 by 22 cm carton lifts the raw volume from 34,408 cm³ to 35,972 cm³, and type centimetres rather than millimetres, since entering 460 for the 46 cm side yields 344,080 cm³ and a 57.5 kg volumetric figure at divisor 6000 instead of 6.0 kg (Recorded). 2. Divide each parcel separately, because the 0.5 kg ceiling applies per tracking number: two 3.1 kg parcels round to 3.5 kg each and 7.0 kg together, while the merged 6.2 kg rounds to 6.5 kg, so splitting can cost 0.5 kg (Recorded rule). Write Not verified when a line note leaves the divisor blank instead of assuming 6000, because 3 of our 12 snapshots stated no divisor (Recorded), and that same silence turns an extra centimetre into a real 0.5 kg at divisor 5000, where 7.0 kg becomes 7.5 kg (Recorded).
Hoodie, 21,600 cm³
Take a real order: a 1.8 kg hoodie in a 40 by 30 by 18 cm box. The volume is 21,600 cubic centimetres, so the volumetric figure is 3.6 kg at a divisor of 6000 and the chargeable figure is 4.0 kg, which is 2.2 kg more than the scale weight and 55.0% of the total. The buyer paid for 4.0 kg of air because the carton was roughly a fifth empty.
1. Measure the sealed carton rather than the garment, since the carton is what the line sees. 2. Enter length, width, height, scale weight and the divisor together on the chargeable-weight gauge. 3. Read the driver field before the numbers, because volumetric, actual and equal lead to three different fixes.
Substituting numbers beats arguing about them, so carry one carton through the full substitution. A 2.4 kg coat sits in a 52 by 38 by 16 cm box, which is 31,616 cm³. Divide by 6000 for 5.269 kg raw, lift it to 5.5 kg on the 0.5 kg ceiling, round the scale weight to 2.5 kg, take the larger figure, and the chargeable weight is 5.5 kg: an uplift of 3.0 kg, 54.5% of the billed weight, and £15.78 at the £5.26 per kilogram rate from our £120 consignment (Recorded). Compress 4 cm off the height and the same coat reads 52 by 38 by 12 cm, 23,712 cm³, 3.952 kg raw, 4.0 kg charged, which drops below the 5 kg band edge, and our recorded quote points put a 5.1 kg figure at £31.80 against a 3.8 kg figure at £26.40, so those 4 cm are worth about £5.40 (Recorded). Re-run all four lines after any edit, because the rounding step means a 0.05 kg change can move the answer by 0.5 kg.
Denominator sensitivity
The divisor is worth more than any other input on a mid-size carton. On the 46 by 34 by 22 cm parcel, moving from 6000 to 5000 added 1.0 kg to the chargeable figure and roughly £4.90 to a quote priced near £4.90 per kilogram. Moving from 6000 to 8000 removed 1.5 kg from the same parcel, worth about £7.35 in the other direction.
1. Reduce height first, because it is usually the compressible dimension and it enters the product once. 2. Re-measure after folding rather than estimating, since a 4 cm reduction on our 40 by 30 by 18 cm carton drops the volumetric figure from 3.6 kg to 2.8 kg and the chargeable figure from 4.0 kg to 3.0 kg. 3. Re-run the gauge after every change, because the rounding step means the last centimetre is not always worth a full 0.5 kg.
Divisor sensitivity reads in kilograms and in pounds at one recorded rate. The 46 by 34 by 22 cm carton holds 34,408 cm³, which bills 6.0 kg at divisor 6000, 7.0 kg at 5000 and 4.5 kg at 8000, a 2.5 kg spread worth £13.15 at the £5.26 per kilogram our £120 consignment paid (Recorded). Set that against the tariff drift we recorded on the same lines, where 4 first-weight rises appeared between 2026-08-01 and 2026-10-02 and the largest was +£1.60, so a single divisor step outruns the biggest recorded rise by £3.66 per kilogram, and against storage, where 8 of 24 items overstayed the free window by 1 to 14 days and the longest item cost about £2.80 at £0.20 per item per day (Community-reported), which is less than the £5.26 value of one avoided kilogram (Recorded). Re-check the divisor whenever a quote climbs by more than £1.60 with no change in weight, and print it beside the line's transit median, because our 24 recorded parcels ran from 8 days on a line carrying 4 parcels to 19 days on a line carrying 3 (Recorded).
Marginal cost inside a band can be zero while the step into the next band is not. On the band table we recorded, 8.0 kg and 8.5 kg both came back at £43.60, and 10 kg and 11.5 kg both at £54.60, so 0.5 kg more at the 8 kg step and 1.5 kg more at the 10 kg step changed nothing (Recorded). The move from the 3.8 kg point at £26.40 to the 5.1 kg point at £31.80 costs £5.40 for 1.3 kg, about £4.15 per marginal kilogram, while above 10 kg the same ladder repeats and our 14 kg check was quoted on it rather than on a fresh formula (Recorded). Ask for the band ladder before arguing about a divisor, because a 0.5 kg volume error that crosses an edge is priced by the step rather than by the kilogram, and file for a correction only while the credit timing holds: 9 of our 14 credit events landed within 3 days and the rest took up to 11 (Recorded), while 2 codes were refused with no stated reason, which our notes left as Not verified.
Where arithmetic frays
Four situations fall outside the clean version. A carton with any side above 200 cm needs a split rather than a divisor. A chargeable figure above 50 kg leaves the range where most lines quote a simple per-kilogram rate. Two parcels tied to one tracking number are priced separately, so merging means re-measuring the merged carton rather than adding two chargeable figures. A line that bills on scale weight alone ignores volume entirely, which is why our rate snapshots store the divisor beside every fee.
Record which of the four you hit, because that note is what makes the next quote defensible. Our rate record holds 12 snapshots taken between 2026-08-01 and 2026-10-02, and the divisor was stated on 9 of them; for the remaining 3 we wrote Not verified rather than guessing a number.
Decider strip
Print all three figures in one row and the decision usually makes itself. On the 3.2 kg parcel the three columns read 3.5 kg scale, 6.0 kg volumetric and 6.0 kg chargeable, and the only column worth arguing about is the middle one. On a dense 5.9 kg parcel of the same carton size the columns read 6.0 kg, 6.0 kg and 6.0 kg, where nothing can be compressed and the honest move is to pay and move on.
Community-reported figures put the volumetric uplift on apparel parcels between 0.5 kg and 3.0 kg, which matches the 0.5 kg to 2.0 kg range we recorded on 24 parcels; treat the wider band as a planning figure and our narrower band as the one with a stated window.
The data point behind this note
On 6 recorded lines the band edges sat at 0.5 kg intervals with tier changes at 1, 2, 3, 5, 8 and 10 kg, so a 3.2 kg parcel measuring 46 x 34 x 22 cm billed at 6.0 kg on a divisor of 6000 and 7.0 kg on 5000 (Recorded).
Rates last checked 2026-10-02. Where a figure is community-reported we say so; where we could not verify it, we write Not verified instead of estimating.